Delayed-start connection for electric motors



Aug. 21, 1945. 5 F 2,383,303

DELAYED-START CONNECTION FOR ELECTRIC MOTORS- Original Filed July 14, 1942 Z 2 flz'recr Heafreceiving Reid/i071 za' Maia/2 L1 5 15 f 12 3 WITNESSES: C INVENTOR 54 DwazflEFrz'zz.

7. f? 1% mm ATTORNEY Patented Aug. 21, 1945 DELAYED-START CONNECTION FOR ELECTRIC MOTORS Dwain E. Fritz, Wapakoneta, Ohio, assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Original application July 14, 1942, Serial No.

1944, Serial No. 530,974

3 Claims. (Cl. 172-279) The present invention relates to self-starting single-phase electric motors and, more particularly, to a connection or control means for delaying the starting of such motors for a predetermined time interval after the motor terminals are energized. The present application is a division of my prior copending application, Serial No. 450,844, filed July 14, 1942, now Patent No. 2,363,310, issued November 21, 194 4.

The delayed-start connection means of the present invention is especially adapted for use with electric motors used for driving fans or blowers in unit heaters. Such heaters require a certain time to become heated after the gas, or other heating means, is ignited or energized, and it is not desirable to start the fan in operation until the heater has become sufliciently heated, so as to avoid blowing cold air into the room. For this reason, it is desirable to delay the starting of the motor which drives the fan for a certain time interval after the heater itself has been energized, and this is most conveniently done by providing for a time delay in the starting means or control of the motor.

The principal object of the present invention is to provide a simple and reliable time-delay connection means for causing an electric motor to start in operation, or to become energized, at a predetermined time after energy has been applied to the motor terminals.

A more specific object of the invention is to provide a time-delay connection for delayed starting of electric motors which includes a thermallyresponsive switch 01' the type in which the contacts are normally open, and which has a heating element for heating it to the temperature at which the contacts close to energize the motor, the switch being mounted in direct heat-receiving relation to the motor, so that when the motor is initially hot the time-delay will be less. This is a desirable feature in unit heater applications, since, if the heater has previously been in operation and still retains some heat, less time is required for it to become sufliciently hot, and it is, therefore, desirable to reduce the time-delay in starting the motor.

A further object of the invention is to provide a delayed-start connection for the control of electric motors which includes a thermally-responsive switch for energizing the motor together with heating means for initially heating the switch to its operating temperature and additional heating means for maintaining the switch at a high enough temperature to cause it to remain in closed Divided and this application April 14,

position, the initial heating means being operative only while the motor is being started.

The invention will be more fully understood from the following detailed description, taken in connection with the accompanying drawing, in which: I

Figures 1 and 2 are schematic diagrams showing diflerent embodiments of the invention.

Figure 1 shows a simple embodiment of the invention for the delayed starting of a single-phase motor I. Any suitable type or single-phase motor may be used in this circuit. The motor shown for the purpose of illustration is'oi the split-phase type, having a main primary winding 2 and an auxiliary or starting primary winding 3, which are displaced from each other on the stator frame of the motor and which are so designed that their currents are displaced in phase. The motor also has a rotor member 4 which carries a suitable secondary winding 5, shown as a squirrel-cage winding. A centrifugal or other type of speedresponsive switch 6 i connected in the circuit of the auxiliary winding 3, and is arranged to be actuated by the rotor 4 when the motor reaches a predetermined speed of rotation, as indicated by the dotted connection 1, so as to disconnect the auxiliary winding 3 after the motor has accelerated to the predetermined speed.

The motor i has line terminals 8 and 9, and a suitable line switch it is provided for connecting the motor to a single-phase supply line Ll, L2. In order to effect the desired time-delay in starting the motor, a thermally-responsive switch it is connected in series in one of the motor terminals. The switch i l is of the so-called inverted" thermostatic type, in which the contacts are normally open and which closes its contacts when the switch is heated to a predetermined temperature. Thus, as shown in the drawing, the switch consists of a bimetallic element 12, which is preferably a disc, or other snap-acting device, and contacts it, which are bridged by the bimetallic element I2 when it is heated above a predetermined temperature. The thermally-responsive switch II is preferably mounted in direct heat-receiving relation to the motor I, as by mounting it directly on the motor frame, and it also has additional heating means for heating it independently of heat from the motor. This heating means preferably comprises an electric heating element I4, which is connected directly across the motor terminals 8 and 8 on the line side of the thermally-responsive switch I I.

The operation of this delayed-start connection should now be apparent. To start the motor, the line switch III is closed to energize the motor terminals 8 and 8 from the supply line, but the motor itself is not energized because the thermally-responsive switch ii is open. Closing of the line switch i0, however, also connects the heating element i4 directly across the line Ll, L2, so that current ilows through the heating element and it begins to generate heat. The heat produced by the heating element l4 raises the temperature of the bimetallic element l2, and after a predetermined time interval, which may be of the order of thirty to sixty seconds, for example, the bimetallic element l2 reaches the temperature at which it operates, and bridges the contacts ll, completing the connection of the motor windings to the line so that the motor starts.

Thus, if. the burner 01 a unit heater is ignited at the same time that the fan motor line switch I is closed, which is the customary arrangement, the motor does not start until a deiinite time interval has elapsed and no air is blown through the heater until it has had time to become heated. In case the heater has previously been in operation, so that some heat still remains in it, the motor will also be warm, and since the theranally-responsive switch II is in direct heatreceiving relation to the motor, it will not take as long for the bimetallic element 12 to become heated to its operating temperature, and the time-delay period is accordingly reduced, which is desirable under these conditions as it does not take the heater as long to become suiiiciently hot.

. Another embodiment of the invention is shown inFig. 2. The motor I shown inthis flgureis identical to that shown in Fig. 1, and its terminals I and I are connected to the line in the same way. The thermally-responsive switch ll connected in series with the lin terminal I is generally similar to the switch H described above, and has an electric heating element ll similar to the heating element H, but it also has a smaller auxiliary heating element H. The heating element It is connected across the line, one end of the heating element ll being connected on the line side 0! the thermally-responsive switch ll, while the other end is connected between the speed-responsive switch and the auxiliary motor-winding 3, as indicated at It. The auxiliary heating element 11 is connected in series with the contacts of the thermally-responsive switch II.

In the operation of this embodiment of the invention, the heating element I. is energized when the line switch i0 is closed, since it is connected directly across the supply line through the speedresponsive switch 8, which is closed when the motor is at rest. The heating element I. therefore, supplies heat to the bimetallic element l2, and when the element I! has reached its operating temperature after a predetermined time delay. the contacts 0! the switch II are closed and the motor starts to accelerate. When the motor has reached a predetermined speed, the speed-responsive switch 6 operates to disconnect the auxiliary winding 3 from the line, and this operation of the switch I also disconnects the heating element it, which is connected on the motor-winding side of the switch I. The auxiliary heating element ll, however, is connected in series with the thermal switch I, so that it is energized by closure 0! the switch contacts. The heating element i1 is designed to provide sumclent heat to keep the temperature of the thermal assasos switch ll above its operating temperature, so that its contacts remain closed and the motor remains connected to the line. It will be seen,

' therefore, that this embodiment of the invention so is picked up and amplified by the large amount of is similar in its operation to that shown in Fig. l, but that the main heating element II is disconnected after the thermal switch II has been initially heated up, anda small auxiliary heating element is used during operation 0! the motor to provide sufllcient heat to keep the thermal switch contacts closed.

The delayed-start connection of the present invention has numerous practical advantages, particularly in its application to unit heater tan motors. A so-called inverted" thermostatic switch is used to effect the time-delay, which is readily available commercially in suitable sizes and ratings, and the heating element which is used with this switch is relatively simple and inexpensive to design and produce. so that the cost of the control system is very low. Animportant advantage of this arrangement is that during the time-delay period the motor windings themselves are not energized. In some delayed-start connections which have previously been used, one or more of the motor windings are energized during the time-delay interval in such a manner that the motor does not start. This energization of the windings causes an objectionable hum, which sheet metal customarily present in unit beaten, so that a distinctly objectionable noise is produced. This disadvantage is entirely eliminated in the present invention, since the motor wind- 88 ings are not energized at all until the motor actually starts. The embodiment of Fig. 2 has the iurther advantage that the main heating element I. is energized only for initially heating the thermal switch and is deenergised when the mo- 40 tor comes up to speed, the small auxiliary heating element I1 being used to maintain the temperature of the switch high enough to keep it closed. Thus, a continuous energy loss in the main heating element is avoided and a material saving is effected. It is apparent, therefore, that the arrangement or the present invention has numerous advantages for any application in which delayed starting of an electric motor is desired, and although it has been described specifically with reference to its use with unit heater motors, it will be understood that its usefulneis not necessarily restricted to this application, but that it may be used to advantage in many other applications where the characteristics described are desirable.

It will be apparent that, although certain speciflc embodiments of the invention have been described for purposes of illustration, the invention is capable of various other embodiments and modifications, and it is to be understood, therefore, that the invention is not limited to the particular arrangements shown, but in its broadest aspects it includes all equivalent embodiments and modifications which come within the scope of the appended claims.

I claim as my invention:

1. A delayed-start electric motor having primary and secondary windings, connection means for connecting said primary windings to a supply line, said connection means including a thermalLvresponsive switch means, said thermally-responsive switch means having contacts which are normally open and being adapted to close its contacts when it is heated to a predetermined temperature, said switch means being located in direct heat-receiving relation to the motor and also having an electric heating element, means for connecting said heating element across the supply line to be energized thereby, means for disconnecting the heating element from the supply line in response to starting of the motor, and auxiliary heating means for heating the thermally-responsive switch during operation or the motor.

2. A delayed-start electric motor having a main primary winding and an auxiliary primary winding, means for connecting said motor to an electric supply line, said connecting means including a thermalLv-responsive switch, said switch having contacts which are normally open and being adapted to close its contacts when it is heated to a predetermined temperature, said thermallymeans tor the thermally-responsive switch, said auxiliary heating means being energized by closure 01' the switch contacts.

- 3. A delayed-start electric motor having a main primary winding and an auxiliary primary winding, means for connecting said motor to an electric supply line, speed-responsive switch means for disconnecting said auxiliary winding when the motor has reached a predetermined speed, said connecting means including a thermally-responsive switch, said switch having contacts which are normally open and being adapted to close its contacts when it is heated to a predetermined temperature, said thermally-responsive switch being located in direct heat-receiving relation to the motor, an electric heating element for heating said switch, said electric heating element being connected between the line side 01' said thermally responsive switch and the motor winding side or said speed-responsive switch, whereby the heating element is connected directly across the supply line when the motor is starting and is disconnected from the line when the speed-responsive switch operates, and an auxiliary heating element for the thermally-responsive switeh connected in series therewith.

DWAIN 1. mm. 

